Intervertebral implant with integrated fixation

ABSTRACT

A system for spinal surgery includes a prosthesis comprising a plurality of bone anchors which engage an intervertebral construct for fusion or motion preservation. The fusion construct comprises a spacer optionally encircled by a jacket. The motion preservation construct may comprise an articulating disc assembly or an elastomeric disc assembly. Any of the constructs may occupy the intervertebral disc space between adjacent vertebrae after removal of an intervertebral disc. The anchors slidingly engage the construct to securely fix the prosthesis to the vertebrae. The anchors and jacket of the fusion construct provide a continuous load path across opposite sides of the prosthesis so as to resist antagonistic motions of the spine.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/857,062, now U.S. Pat. No. 9,788,968, filed on Sep. 17,2015, which is a continuation of U.S. patent application Ser. No.13/723,360, now U.S. Pat. No. 9,138,275, filed on Dec. 21, 2012, whichis a continuation of U.S. patent application Ser. No. 12/640,816, nowU.S. Pat. No. 8,349,015, filed on Dec. 17, 2009, which claims thebenefit of the filing dates of U.S. Provisional Patent Application No.61/151,701 filed Feb. 11, 2009, U.S. Provisional Patent Application No.61/232,705 filed Aug. 10, 2009, U.S. Provisional Patent Application No.61/232,745 filed Aug. 10, 2009, U.S. Provisional Patent Application No.61/257,734 filed Nov. 3, 2009, and U.S. Provisional Patent ApplicationNo. 61/257,667 filed Nov. 3, 2009, all of the disclosures of which arehereby incorporated herein by reference.

BACKGROUND OF THE INVENTION The Field of the Invention

The invention relates to spinal surgery. More precisely, the presentinvention relates to intervertebral prostheses implanted following atleast partial disc excision.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of the intervertebral fusion prosthesis ofFIG. 7, comprising a spacer, a jacket, and two anchors;

FIG. 2A is a lateral view of the intervertebral fusion prosthesis ofFIG. 7; and FIG. 2B is a cranial view of the intervertebral fusionprosthesis of FIG. 2A;

FIG. 3A is an anterior view of the spacer of FIG. 7; and FIG. 3B is acranial view of the spacer of FIG. 3A;

FIG. 4A is an anterior view of the jacket of FIG. 7; and FIG. 4B is acranial view of the jacket of FIG. 4A;

FIG. 5 is an exploded perspective view of the spacer and jacket of FIG.7;

FIG. 6A is a lateral view of the anchor of FIG. 7; and FIG. 6B is acranial (or caudal) view of the anchor of FIG. 6A;

FIG. 7 is a perspective view of an intervertebral fusion prosthesisinserted into an intervertebral space between two adjacent cervicalvertebrae;

FIG. 8 is a perspective view of an alternate embodiment of anintervertebral fusion prosthesis comprising a spacer, a jacket, and twoanchors;

FIG. 9 is an exploded perspective view of a motion-preserving total discreplacement prosthesis;

FIG. 10 is a lateral view of an alternate embodiment of amotion-preserving total disc replacement prosthesis;

FIG. 11 is a perspective view of an alternate embodiment of anintervertebral fusion prosthesis, comprising a spacer, a jacket, andfour anchors;

FIG. 12 is an anterior view of the intervertebral fusion prosthesis ofFIG. 11;

FIG. 13 is a cranial view of the intervertebral fusion prosthesis ofFIG. 11;

FIG. 14 is a perspective view of the spacer of FIG. 11;

FIG. 15A is a cranial view of the spacer of FIG. 11; and FIG. 15B is ananterior view of the spacer of FIG. 15A;

FIG. 16 is a perspective view of the jacket of FIG. 11;

FIG. 17A is a cranial view of the jacket of FIG. 11; and FIG. 17B is ananterior view of the jacket of FIG. 17A;

FIG. 18 is a perspective view of the intervertebral fusion prosthesis ofFIG. 11, implanted in an intervertebral space between two adjacentlumbar vertebrae;

FIG. 19A is a postero-lateral view of an alternate embodiment of anintervertebral fusion prosthesis; FIG. 19B is a caudal view of theintervertebral fusion prosthesis of FIG. 19A; and FIG. 19C is ananterior view of the intervertebral fusion prosthesis of FIG. 19A;

FIG. 20A is an anterior perspective view of an alternate embodiment ofan intervertebral fusion prosthesis; FIG. 20B is an anterior perspectiveview of the jacket of FIG. 20A; FIG. 20C is an anterior perspective viewof the spacer of FIG. 20A; FIG. 20D is a lateral view of the anchor ofFIG. 20A; and FIG. 20E is an anterior perspective view of the anchor ofFIG. 20A;

FIG. 21A is a lateral view of an alternate embodiment of an anchor; andFIG. 21B is an anterior (or proximal) view of the anchor of FIG. 21A;

FIG. 22A is a perspective view of an alternate embodiment of anintervertebral fusion prosthesis; FIG. 22B is a perspective view ofanother alternate embodiment of an intervertebral fusion prosthesis;FIG. 22C is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis; FIG. 22D is a perspective view of yetanother alternate embodiment of an intervertebral fusion prosthesis;FIG. 22E is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis; FIG. 22F is a perspective view of yetanother alternate embodiment of an intervertebral fusion prosthesis;FIG. 22G is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis; FIG. 22H is a perspective view of yetanother alternate embodiment of an intervertebral fusion prosthesis;FIG. 22I is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis; FIG. 22J is a perspective view of yetanother alternate embodiment of an intervertebral fusion prosthesis;FIG. 22K is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis; FIG. 22L is a perspective view of yetanother alternate embodiment of an intervertebral fusion prosthesis; andFIG. 22M is a perspective view of yet another alternate embodiment of anintervertebral fusion prosthesis;

FIG. 23A is a perspective view of an alternate embodiment of anintervertebral fusion prosthesis sized and shaped to be inserted in onelateral side of an intervertebral space, comprising a spacer, a jacketand two anchors; and FIG. 23B is a perspective view of an alternateembodiment of an intervertebral fusion prosthesis, comprising a spacerand two screw-type anchors;

DETAILED DESCRIPTION

The present invention advances the state of the art by providingintervertebral prostheses with anchors to secure the prostheses to bone.

In this specification, the following terms are used with the specifieddefinitions.

Antagonistic spinal motion is defined as substantially identical spinalmotions in opposite directions. Therefore, spinal flexion and extensionis an example of antagonistic spinal motions. Other examples includeright and left axial rotation, right and left lateral bending, andanterior and posterior translation. In this specification, antagonisticspinal motion is equivalent to opposite spinal motion.

A patent opening is defined as an unobstructed opening extending throughall identified features or structures.

An acute angle is defined as an angle greater than 0 degrees and lessthan 90 degrees. Two components oriented at an acute relative angle maynot be parallel or perpendicular to each other. A compound angle is theresultant angle projected from two angles lying in mutuallyperpendicular planes.

Foliate is defined as shaped like a leaf. Leaves occur in a multitude ofshapes, or two-dimensional profiles. Leaves also have thickness and aretherefore three-dimensional structures. Certain leaves are normallycreased or puckered so that they have a pronounced three-dimensionalshape. The three-dimensional aspect is included in the presentdefinition of foliate.

Sagittate is defined as shaped like an arrowhead. Arrowheads, moreproperly termed projectile points, occur in a multitude of shapes, ortwo-dimensional profiles. Projectile points also have thickness and aretherefore three-dimensional structures. The three-dimensional attributeis included in the present definition of sagittate. Projectile pointsalso typically comprise a pointed tip, sharpened edges, and a blunttrailing end. At least these attributes are included in the presentdefinition of sagittate.

Referring to FIGS. 1-2, a prosthesis 110 according to the presentinvention is shown. The prosthesis 110 comprises an intervertebralspacer 112, a jacket 114, and multiple anchors 116, or bone engagementelements. The present embodiment includes two anchors 116 disposed onopposite sides of the spacer 112. The spacer 112 may fill a portion ofan intervertebral disc space between adjacent vertebrae after removal ofa portion of an intervertebral disc. The jacket 114 may surround thespacer 112 in approximately the same orientation that an intact annulusfibrosus surrounds a natural intervertebral disc. The anchors 116 mayslide into engagement with the spacer 112 and the jacket 114 to rigidlyconnect the spacer 112 to the vertebral bodies.

Referring to FIG. 3, the spacer 112 is illustrated in a front view (FIG.3A) and a top view (FIG. 3B). The spacer 112 may comprise a top side118, a bottom side 120 opposite the top side 118, a leading side 124, atrailing side 122 opposite the leading side 124, and two lateral sides126 extending between the leading 124 and trailing 122 sides. In otherwords, the spacer 112 may comprise a general three-dimensional body. Thepresent embodiment of the spacer 112 has a generally oval shape in thetop view. Alternatively, the spacer 112 may be square, rectangular,circular, elliptical, kidney-shaped, or any other shape in the top view.The top and bottom sides 118, 120 of the spacer 112 may be flat,concave, convex, or any other shape in the front view (FIG. 3A) orlateral view (FIG. 2A). In particular, the top and bottom sides 118, 120of the spacer 112 may be curved or angled to maintain or restore ananatomically appropriate lordotic or kyphotic angle in the lateral view.In certain embodiments, the various sides of the spacer 112 may blendtogether to a greater or lesser degree.

The spacer 112 may comprise an interconnection feature extending acrossthe top 118 or bottom side 120. The interconnection feature is shapedand sized to mate with a corresponding interconnection portion of theanchor 116. In the present embodiment, the interconnection feature is adovetail slot 146 between the leading and trailing sides 124, 122, asshown most clearly in FIG. 5. A first dovetail slot 146 extends acrossthe top side 118 and a second dovetail slot 146 extends across thebottom side 120. Alternatively, the interconnection feature couldcomprise a T-slot, slide, keyways, ratchets, pins, press-fit components,or threads. The interconnection feature could alternatively comprise aprotruding feature corresponding to any of the undercut featurespreviously listed.

The spacer 112 may comprise a ridge 128, or shelf, extending along alateral side 126 adjacent to the top 118 or bottom side 120. In theembodiment shown, the spacer 112 comprises bilateral ridges 128 adjacentto the bottom side 120. It can be appreciated from FIG. 3 that theridges 128 increase the surface area of the bottom side 120 relative tothe top side 118.

The spacer 112 may optionally have one or more cavities 130 extendingthrough the top and bottom sides 118, 120 to contain bone graft materialor to serve as channels for bone growth. Each cavity 130 may extendunobstructed through the spacer 112 so as to comprise a patent openingthrough the spacer 112. In the present embodiment, the spacer 112 hasbilateral cavities 130 separated by a central web 148 and encircled byan annular wall 150. Alternatively, the spacer may have no cavity 130.

The spacer 112 may have one or more instrument connection features onthe trailing side 122. In the present embodiment, the spacer 112 has afirst hole 154 and a second hole 156 through the wall 150 on thetrailing side 122. One or both of the holes 154, 156 may be threaded orprovided with other connection means, such as a bayonet socket, notches,or undercuts. In the present embodiment, the first hole 154 is threaded.Alternatively, the instrument connection feature may be a protrudingfeature such as a post or tab. It is contemplated that the spacer maylack an instrument connection feature altogether.

The top and bottom sides 118, 120 of the spacer 112 may be roughened toprevent in-vivo migration. Alternately, the top and bottom sides 118,120 of the spacer 112 may be provided with an alternating pattern ofridges 152 and grooves 153, teeth, or other structured surfaceenhancements. FIG. 2A shows ridges 152 and grooves 153 from a lateralview.

The spacer 112 may comprise radiolucent polyetheretherketone (PEEK) orpolyaryletherketone (PAEK). Alternatively, the spacer 112 may comprise amaterial that is only partially radiolucent, so that the spacer 112 maybe visualized radiographically without obscuring a view of anydeveloping intervertebral bone fusion mass. Alternatively, the structureof the spacer 112 may be manipulated to produce partial radiolucence,such as by forming a radiopaque material with grooves, controlledporosity, or other means. In an alternate embodiment, the spacer 112 maycomprise autograft bone, allograft bone, or bone graft substitute. Thespacer 112 may alternatively comprise metal, ceramic, glass, polymer, orany other material known for use in the human body. The spacer 112 mayalso comprise one or more surface treatments to encourage bonyattachment, such as porous coating, plasma spray coating,hydroxyapatite, or tricalcium phosphate.

Referring to FIG. 4, the jacket 114 is illustrated in a front view (FIG.4A) and a top view (FIG. 4B). The jacket 114 comprises an annular wall132 extending between a top side 158 and a bottom side 160 andcomprising a leading portion 136, a trailing portion 134 opposite theleading portion 136, and two side portions 138 extending between theleading 136 and trailing 134 portions. With reference to FIGS. 1-2, itcan be appreciated that the leading 136 and trailing 134 portions of thejacket 114 may extend proximate the top and bottom sides 118, 120 of thespacer 112 when the spacer 112 and jacket 114 are assembled together.However, the side portions 138 may be spaced apart from the top andbottom sides 118, 120. This arrangement may afford an unobstructedpost-operative lateral view of any developing bone fusion mass proximatethe top and bottom sides 118, 120 of the spacer 112. The presentembodiment of the jacket 114 has a generally oval shape in the top view,corresponding closely to the shape of the spacer 112 in the top view. Itis contemplated that alternatively shaped jackets may be constructed tocorrespond closely to the alternative spacer shapes describedpreviously. It is further contemplated that the jacket 114 may be shapedto correspond closely to selected portions of the spacer 112, with a gapbeing present around the remaining interface. This approach may simplifyfabrication of the spacer 112 and the jacket 114 by permit largermanufacturing tolerances, at least in the regions where a gap existsbetween the spacer 112 and the jacket 114.

The jacket 114 may comprise an interconnection feature extending acrossthe top 156 or bottom side 158. Preferably, the interconnection featureis identical to the interconnection feature of the spacer 112. In thepresent embodiment, the interconnection feature is a dovetail slot 162between the leading and trailing portions 136, 134, as shown mostclearly in FIG. 5. A first dovetail slot 162 extends across the top side156 and a second dovetail slot 162 extends across the bottom side 158.The interconnection feature on the jacket 114 may comprise any of thealternative configurations set forth previously with regard to theinterconnection feature on the spacer 112.

The jacket 114 may have a window 140 through the side portions 138through which a developing bone fusion mass may be radiographicallyobserved post-operatively. The window 140 may extend unobstructedthrough the jacket 114 so as to comprise a patent opening across thejacket 114.

The jacket 114 may have one or more instrument connection features onthe trailing portion 134. In the present embodiment, the jacket 114 hasa first hole 164 and a second hole 166 through the wall 132 on thetrailing portion 134. One or both of the holes 164, 166 may be threaded.In the present embodiment, the first hole 164 is threaded. The jacketmay comprise alternative instrument connection features, or noinstrument connection feature, as described previously for the spacer112.

The jacket 114 may be made of metal, ceramic, glass, polymer, or anyother structural material known for use in the human body. The jacket114 may also comprise one or more surface treatments to encourage bonyattachment, such as porous coating, plasma spray coating,hydroxyapatite, or tricalcium phosphate. In an alternate embodiment, thejacket 114 may comprise autograft bone, allograft bone, or bone graftsubstitute.

Referring to FIG. 5, an exploded perspective view illustrates the jacket114 and the spacer 112. The jacket 114 may fit snugly over an outerperimeter surface 142 of the spacer 112 so that the spacer 112 andjacket 114 form a spacer assembly 144. Referring to FIGS. 3-5, when thespacer 112 and the jacket 114 are assembled, the leading portion 136 ofthe jacket 114 is adjacent to the leading side 124 of the spacer 112,the trailing portion 134 of the jacket 114 is adjacent to the trailingside 122 of the spacer 112, the side portions 138 of the jacket 114 areadjacent to the lateral sides 126 of the spacer 112, the top side 158 ofthe jacket 114 is proximate the top side 118 of the spacer 112, and thebottom side 160 of the jacket 114 is proximate the bottom side 120 ofthe spacer 112. In this case, the ridge 128 on the spacer 112 may abut aside portion 138 of the jacket 114 when the spacer 112 and jacket 114are assembled.

With reference to FIGS. 3-5, the spacer assembly 144 may have aninterconnection feature that extends across the spacer 112 and thejacket 114. In the present embodiment, the spacer assembly 144 comprisestwo interconnection features, one extending across the top side 118 ofthe spacer 112 and one extending across the bottom side 120 of thespacer 112. Each interconnection feature comprises the dovetail slot 146of the spacer 112 which aligns with the dovetail slot 162 in the jacket114 so as to form a single continuous interconnection feature across thespacer assembly 144, as is most clearly seen in FIG. 1. The dovetailslot 146, 162 captures the interconnection portion of the anchor 116 andtransmits tension, compression, shear, torsion, and bending loadsbetween the anchor 116 and the spacer. In the present embodiment, spinalloads are distributed from one vertebra to another through the anchors116 and across the leading and trailing portions 136, 134 of the jacket114. When this embodiment is implanted from an anterior approach, theleading portion 136 of the jacket 114 is in the posterior portion of theintervertebral space and the trailing portion 134 of the jacket 114 isin the anterior portion of the intervertebral disc space. With thisarrangement, the prosthesis 110 may replicate the strength and stiffnessof the natural anterior and posterior longitudinal ligaments to providesuperior fixation of adjacent vertebral bodies.

Referring to FIG. 6, the anchor 116 is illustrated in a side view (FIG.6A) and a top view (FIG. 6B). The anchor 116 may be generally elongatewith a leading end 168 and a trailing end 170 opposite the leading end168. Anchors of different sizes and shapes may be provided.

The anchor 116 may comprise an interconnection portion extending betweenthe leading and trailing ends 168, 170. The interconnection portion maybe shaped and sized to mate with the interconnection feature previouslydescribed for the spacer assembly 144, so as to slidably connect theanchor 116 to the spacer assembly 144. In the present embodiment, theinterconnection portion of the anchor 116 is a dovetail beam 172. Whenthe anchor 116 is fully engaged with the spacer assembly 144, thedovetail beam 172 engages the leading portion 136 and trailing portion134 of the jacket 114 so that load may be transmitted between the anchor116 and the jacket 114 across opposite sides of the jacket 114. Theinterconnection portion may alternatively comprise a T-rail, slide, key,ratchets, pins, press-fit components, or threads. The interconnectionfeature could alternatively comprise an undercut feature correspondingto any of the protruding features previously listed.

The anchor 116 may comprise a stop feature that prevents the anchor 116from advancing too far into the spacer assembly 144 at the time ofimplantation, or migrating toward the leading portion 136 of the jacket114 post-operatively. In the present embodiment, the stop feature is aflange 174, or enlarged tip, integrated on the dovetail beam 172 at thetrailing end 170. The outer profile of the flange 174 is larger than theprofile of the mating dovetail slot 162 in the jacket 114. Therefore,the flange 174 cannot pass into the dovetail slot 162. The flange 174may taper or flare from the dovetail beam 172 toward the trailing end170. A matching chamfer 176 may be present around the dovetail slot 162,so that the flange 174 may be at least partially recessed within thetrailing portion 134 of the jacket wall 132. The congruent taperedsurfaces of the flange 174 and the chamfer 176 provide a more uniformstress distribution than may be present with point-to-point orpoint-to-surface contact. This maximizes the load bearing capability ofthe flange 174 and chamfer 176.

The anchor 116 may comprise a locking feature that prevents the anchorfrom migrating toward the trailing portion 134 of the jacket 114post-operatively. In the present embodiment, the locking feature is aflexible tab 178 integrated on the dovetail beam 172 proximate thetrailing end 170, as best seen in FIG. 9. As the dovetail beam 172advances into the spacer assembly 144, the tab 178 contacts the trailingportion 134 of the jacket 114 and elastically deforms toward thedovetail beam 172. As the dovetail beam 172 advances further into thespacer assembly 144, the tab 178 slides past the trailing portion 134 ofthe jacket 114 and springs away from the dovetail beam 172 so that thetip 180 of the tab 178 makes surface-to-surface contact with an innersurface 182 of the jacket 114. Thus, the tab 178 prevents the anchor 116from migrating toward the trailing portion 134 of the jacket 114post-operatively. The locking feature may alternatively snap intoengagement with the trailing side 122 of the spacer 112. The lockingfeature may alternatively be integrated into the jacket 114 or into thespacer 112.

The anchor 116 may comprise a fixation portion that rigidly secures theanchor 116 to a bone. More specifically, the fixation portion may resistaxial tensile and compressive forces resulting from, for example, spinalflexion and extension or right and left lateral bending. The fixationportion may extend between the leading and trailing ends 168, 170 of theanchor, and may be spaced apart from the interconnection portiondescribed previously. In the present embodiment, the fixation portion isa plate 184 extending between the leading and trailing ends 168, 170 ofthe anchor. The plate 184 comprises two broad surfaces, a top side 186and a bottom side 188 opposite the top side 186. In the presentembodiment, the bottom side 188 of the plate 184 is oriented to squarelyface the dovetail beam 172.

Referring to FIG. 6B, the present embodiment of the plate 184 has a topview profile that resembles a leaf or an arrowhead. Thus, the plate 184can be described as foliate (shaped like a leaf) or sagittate (shapedlike an arrowhead). The plate 184 tapers to a point 190 at the leadingend 168 and terminates in a blunt edge 192 at the trailing end 170. Thepointed leading end 168 reduces the magnitude of the force required forinsertion and to minimize collateral damage to the vertebral body. Anoptional window 191 may pierce the plate 184.

The present embodiment of the plate 184 is flat in the side view, asseen in FIG. 6A. Alternatively, plate 184 could be bent, curved,rounded, or otherwise shaped to resemble a “T”, “L,” “O”, “Y”, “V”,rectangle, circle, oval, concave, convex, and variations thereof in theside view, or alternately, in a view from the leading end 168 ortrailing end 170.

Referring to FIG. 6A, with brief reference to FIG. 1, the presentembodiment of the plate 184 is sharpened around at least a portion ofits profile to produce a cutting edge 194 capable of cutting throughbone. More precisely, the cutting edge 194 may extend along lateralsides of the plate to the point 190, while the blunt edge 192 maypreferably be left unsharpened to resist migration after insertion.Alternatively, the cutting edge 194 may extend only along the portion ofthe profile that faces toward the leading end 168. The cutting edge 194may be V-shaped, convex, hollow ground, or any other cutting edge shape.In a preferred embodiment, the cutting edge 194 may be produced with acurved face adjacent the bottom side 188 and a flat face adjacent thetop side 186. In an alternative embodiment, the plate 184 may besharpened asymmetrically so that the cutting edge 194 is located closerto the top side 186 than to the bottom side 188. By producing thecutting edge 194 with a curved face and a flat face, or byasymmetrically locating the cutting edge 194 proximate to the top side186, the plate 184 may be biased to track along a path that diverges atleast slightly from the path taken by the dovetail beam 172 as theanchor 116 slides into engagement with the spacer assembly 144 andadjacent vertebrae. In other words, this configuration naturally biasesthe anchor 116 to lift away from the dovetail beam 172 when the plate184 is inserted into bone. When two or more anchors 116 according tothis preferred embodiment are inserted on opposite sides of the spacerassembly 144 to engage adjacent vertebrae, the vertebrae are compressedagainst the spacer assembly 144 as the anchors 116 are advanced.Additionally, the cutting edge 194 may be interrupted by saw teeth orserrations 195 to resist migration after insertion.

The anchor 116 may comprise a leg 196 extending generallyperpendicularly between the interconnection portion and the fixationportion. In the present embodiment, a first leg 196 extends between thedovetail beam 172 and the plate 184. The first leg 196 is disposedtoward the leading end 168 of the anchor 116. A second leg 198 extendsbetween the dovetail beam 172 and the plate 184 and is disposed towardthe trailing end 170 of the anchor 116. This arrangement provides awindow 199, or patent opening, between the legs 196, 198, so that anydeveloping bone fusion mass may be radiographically observedpost-operatively. A cutting edge 197 capable of cutting through bone maybe present on the first leg 196, on a side proximate the leading end 168of the anchor 116. Alternatively, the leg may be configured to avoidpenetrating bone at all.

The anchor 116 may alternatively comprise any of a variety of featuresto resist migration after insertion, such as teeth, keels, prongs, fishhooks, or barbs to engage the bone or the spacer 112.

The anchor 116 may be made of metal, ceramic, glass, polymer, or anyother structural material known for use in the human body. The anchor116 may also comprise one or more surface treatments to encourage bonyattachment, such as porous coating, plasma spray coating,hydroxyapatite, or tricalcium phosphate. In an alternate embodiment, theanchor 116 may comprise autograft bone, allograft bone, or bone graftsubstitute.

Referring to FIG. 7, the prosthesis 110 is shown implanted in anintervertebral space 6 between adjacent cervical vertebrae 2, 4. It canbe appreciated that the spacer 112 of prosthesis 110 may be sized andshaped to at least partially fill an intervertebral disc space betweenadjacent vertebrae at any level of the spine after removal of at least aportion of an intervertebral disc.

Methods of implanting the intervertebral fusion prosthesis 110 in thecervical spine from an anterior surgical approach will now be describedwith reference to FIG. 7. It is understood that the same or similarmethods may be employed to implant the prosthesis 110 at any level ofthe spine, and from any surgical approach, without departing from thescope of the present invention. More specifically, it is contemplatedthat prosthesis 110 may be implanted from an anterior, posterior,lateral, transforaminal, or other surgical approach.

At least a portion of an intervertebral disc 8 (not shown) betweenadjacent cervical vertebrae 2, 4 may be removed from the intervertebraldisc space 6, using tools and techniques known in the art. Substantiallyall of the disc 8 may be removed in the present embodiment.

The spacer assembly 144 having a size and shape corresponding to thedisc space 6 may be selected from a kit comprising spacer assemblies ofvarious sizes and shapes. The spacer assembly 144 may be oriented sothat the top side 118 of the spacer 112 faces superiorly and the bottomside 120 of the spacer 112 faces inferiorly. The spacer assembly 144 maybe further oriented so that the leading side 124 of the spacer 112 facesposteriorly and the trailing side 122 of the spacer 112 facesanteriorly. The spacer assembly 144 is inserted into the disc space 6between vertebrae 2, 4 from anterior to posterior until the spacerassembly 144 is generally concentric with the adjacent vertebral bodiesof vertebrae 2, 4.

A first anchor 116 having a size and shape corresponding to the discspace 6 and vertebral bodies of vertebrae 2, 4 may be selected from akit comprising anchors of various sizes and shapes. The anchor 116 maybe oriented so that the plate 184 faces superiorly and the dovetail beam172 faces inferiorly. The anchor 116 may be further oriented so that theleading end 168 faces posteriorly, the trailing end 170 facesanteriorly, and the dovetail beam 172 is collinear with the dovetailslot 162 across the top side 158 of the jacket 114 and the dovetail slot146 across the top side 118 of the spacer 112. The dovetail beam 172 ofthe anchor 116 is inserted into the dovetail slots 162, 146 fromanterior to posterior until the dovetail beam 172 engages the leadingportion 136 and trailing portion 134 of the jacket 114, the flange 174abuts the chamfer 176, and the tab 178 snaps behind the inner surface182 of the jacket 114.

A second anchor 116 may be selected from the kit and oriented so thatthe plate 184 faces inferiorly, the dovetail beam 172 faces superiorly,the leading end 168 faces posteriorly, the trailing end 170 facesanteriorly, and the dovetail beam 172 is collinear with the dovetailslots 162, 146 across the bottom sides 160, 120 of the jacket 114 andspacer 112. The dovetail beam 172 of the anchor 116 is inserted asdescribed previously.

In a preferred embodiment, the spacer assembly 144 is placed in theintervertebral space 6 first, followed by anchors 116 which secure thespacer assembly 144 to the vertebral bodies of adjacent vertebrae 2, 4.Alternatively, the spacer assembly 144 and anchors 116 may bepre-assembled and subsequently inserted into the disc space 6 as a unit,or the anchors 116 may be inserted into the vertebral bodies ofvertebrae 2, 4, followed by the spacer assembly 144.

Referring to FIG. 7, the prosthesis 110 may provide a stable constructby ensuring both anterior and posterior rigid fixation of the adjacentvertebral bodies of vertebrae 2, 4, when implanted from an anteriorapproach. In general, the more rigid the fixation, the more conducivethe environment is to bony fusion. Traditional spinal fusion proceduresform stable constructs by relying upon a spacer that is used incombination with a plate or a rod and screw system. The currentembodiment may provide the same stability as a traditional spinal fusionconstruct, but with reduced surgical time as well as the potential forreduced complications associated with secondary hardware outside of theintervertebral space. Newer products on the market only provide anteriortensile load paths, through the use of bone screws or keels. The presentembodiment of prosthesis 110 utilizes sliding anchors 116 that connectthe anterior and posterior ends of the spacer assembly 144 to theadjacent vertebral endplates. This non-screw based approach leads to amore symmetric stiffness profile of the construct, as well as a reducedradiographic profile. Additionally, the prosthesis 110 may be implantedwithout using instruments at extreme oblique angles, which reducescomplexity for the surgeon.

Referring to FIG. 8, an alternate embodiment of an intervertebral fusionprosthesis 210 is shown. The prosthesis 210 comprises an intervertebralspacer 212, a jacket 214, and two anchors 216 disposed on opposite sidesof the spacer 212. The anchors 216 slidingly engage the jacket 214 andspacer 212 in the manner described previously.

Referring to FIG. 9, a motion-preserving total disc replacementprosthesis 310 is illustrated in an exploded perspective view. Theprosthesis 310 comprises a convex articular component 312, a concavearticular component 314 shaped to articulate with the convex articularcomponent 312, and two anchors 316 disposed on opposite sides of theprosthesis 310. The anchors 316 slidingly engage the convex articularcomponent 312 and concave articular component 314 in the mannerdescribed previously. In the present embodiment, the anchors 316 provideprimary fixation of the prosthesis 310 to adjacent vertebrae. Thearticular components 312, 314 may each comprise an articular surfaceintegrally formed with an endplate, or alternatively, the articularcomponents may each comprise an articular surface secured to a separateendplate.

Referring to FIG. 10, an alternate embodiment of a motion-preservingtotal disc replacement prosthesis 410 is illustrated in a lateral view.The prosthesis 410 comprises two endplates 412, an elastomeric disccomponent 414 disposed between the endplates 412, and two anchors 416disposed on opposite sides of the prosthesis 410. The anchors 416slidingly engage the endplates 412 in the manner described previously.

Referring to FIGS. 11-13, an alternate embodiment of an intervertebralfusion prosthesis 510 is illustrated. Prosthesis 510 comprises a spacer512, a jacket 514, and four anchors 516.

Referring to FIGS. 14-15, the spacer 512 is illustrated in a perspectiveview (FIG. 14), a top view (FIG. 15A) and a front view (FIG. 15B). Thespacer 512 comprises a top side 518, a bottom side 520 opposite the topside 518, a leading side 524, a trailing side 522 opposite the leadingside 524, and two lateral sides 526 extending between the leading 524and trailing 522 sides. The spacer 512 has a generally kidney-shapedprofile in the top view. The top and bottom sides 518, 520 of the spacer512 are gently contoured in the front view.

In the present embodiment, the spacer 512 comprises four dovetail slots546 between the leading and trailing sides 524, 522, as shown mostclearly in FIG. 14. Two dovetail slots 546 extend across the top side518 and two dovetail slots 546 extend across the bottom side 520. Withreference to FIG. 15A, the dovetail slots 546 on the top side 518 aredisposed at an acute angle relative to each other in a first planeparallel to the top side 518, such as the top view plane. The dovetailslots 546 are farther apart at the leading side 524 and closer togetherat the trailing side 522. With reference to FIG. 15B, the dovetail slots546 on the top side 518 are also disposed at an acute angle relative toeach other in a second plane perpendicular to the first plane, such asthe front view plane. An open end 545 of each dovetail slot 546 isfarther apart at the top side 518 and a closed end 547 of each dovetailslot 546 is closer together deep within the spacer 512. It can also beappreciated that the closed ends 547 of the dovetail slots are mutuallytilted at an acute angle. Thus, the dovetail slots 546 on the top side518 may be said to be oriented at a compound acute relative angle. Thedovetail slots 546 on the bottom side 520 are similarly oriented in thisembodiment.

The spacer 512 comprises a ridge 528, or shelf, extending along alateral side 526 adjacent to the bottom side 520.

The spacer 512 has three cavities 530 extending through the top andbottom sides 518, 520 to contain bone graft material or to serve aschannels for bone growth. Each cavity 530 extends unobstructed throughthe spacer 512 so as to comprise a patent opening through the spacer512. The cavities 530 are separated by two central webs 548 andencircled by an annular wall 550.

The spacer 512 has a hole 554 through the wall 550 on the trailing side522. The hole 554 may be threaded or provided with other connectionmeans, as described previously.

Referring to FIGS. 16-17, the jacket 514 is illustrated in a perspectiveview (FIG. 16), a top view (FIG. 17A) and a front view (FIG. 17B). Thejacket 514 comprises an annular wall 532 extending between a top side558 and a bottom side 560 and comprising a leading portion 536, atrailing portion 534 opposite the leading portion 536, and two sideportions 538 extending between the leading 536 and trailing 534portions. With reference to FIGS. 11-12, it can be appreciated that theleading 536 and trailing 534 portions of the jacket 514 may extendproximate the top and bottom sides 518, 520 of the spacer 512 when thespacer 512 and jacket 514 are assembled together. However, the sideportions 538 may be spaced apart from the top and bottom sides 518, 520.The jacket 514 (FIG. 17A) corresponds closely to the shape of the spacer512 (FIG. 15A) in the top view.

The jacket 514 comprises four dovetail slots 562 between the leading andtrailing portions 536, 534, as shown most clearly in FIG. 16. Twodovetail slots 562 extend across the top side 558 and two dovetail slots562 extend across the bottom side 560. The dovetail slots 562 areoriented at a compound acute relative angle as described previously forthe spacer 512.

The jacket 514 has a window 540 through the side portions 538. Thewindow 540 extends unobstructed through the jacket 514 so as to comprisea patent opening across the jacket 514.

The jacket 514 has a hole 564 through the wall 532 on the trailingportion 534. The hole 564 may be threaded or provided with otherconnection means, as described previously

Referring to FIGS. 14 and 16, the jacket 514 is sized and shaped to fitsnugly over an outer perimeter surface 542 of the spacer 512 so that thespacer 512 and jacket 514 form a spacer assembly 544, shown in FIG. 11.When the spacer 512 and the jacket 514 are assembled, the leadingportion 536 of the jacket 514 is adjacent to the leading side 524 of thespacer 512, the trailing portion 534 of the jacket 514 is adjacent tothe trailing side 522 of the spacer 512, the side portions 538 of thejacket 514 are adjacent to the lateral sides 526 of the spacer 512, thetop side 558 of the jacket 514 is proximate the top side 518 of thespacer 512, and the bottom side 560 of the jacket 514 is proximate thebottom side 520 of the spacer 512. In this case, the ridge 528 on thespacer 512 may abut a side portion 538 of the jacket 514 when the spacer512 and jacket 514 are assembled.

With reference to FIG. 11, the dovetail slots 546 on the top side 518 ofthe spacer 512 align with the dovetail slots 562 on the top side 558 ofthe jacket 514 to form continuous collinear interconnection featureswhen the spacer 512 and the jacket 514 are assembled together.Similarly, the dovetail slots 546 on the bottom side 520 of the spacer512 align with the dovetail slots 562 on the bottom side 560 of thejacket 514 to form continuous collinear interconnection features whenthe spacer 512 and the jacket 514 are assembled together.

The interconnection features on the spacer assembly 544 may beconfigured in many alternative embodiments. Considering a top side ofthe spacer assembly 544, there may be one or more interconnectionfeatures distributed symmetrically or asymmetrically across the spacerassembly 544. The interconnection features may be oriented parallel toeach other, or at an acute angle in one or more planes of reference.Considering the top and bottom sides of the spacer assembly 544, thenumber of interconnection features may be equal or unequal. It can beappreciated that the number, distribution, and orientation ofinterconnection features on the spacer assembly 544 will correspond atleast in part to the number, distribution, and orientation of anchors516 present in prosthesis 510.

By orienting the anchors 516 at an acute relative angle in one or moreplanes, the prosthesis 510 may experience less post-operative migration.The compound acute relative angle discussed previously may also minimizethe risk of bone fracture due to multiple stress risers created byinserting the anchors 516 into the bone.

Referring to FIGS. 11-12, the anchor 516 may be similar in design andconstruction to anchor 116 described previously.

Referring to FIG. 18, the prosthesis 510 is shown implanted in anintervertebral space 16 between adjacent lumbar vertebrae 12, 14. It canbe appreciated that the spacer 512 of prosthesis 510 may be sized andshaped to at least partially fill an intervertebral disc space betweenadjacent vertebrae at any level of the spine after removal of at least aportion of an intervertebral disc.

The method of implanting prosthesis 510 from an anterior approach issimilar to that described previously for prosthesis 110. However, twoanchors 516 are inserted into each adjacent vertebral body of vertebrae12, 14, so that prosthesis 510 comprises a total of four anchors 516when fully implanted. Because the anchors 516 are inserted in line withthe dovetail slots 562, 546, the anchors 516 may be inserted at an angleto the approach used to insert the spacer assembly 544.

Referring to FIGS. 19-20, an alternate embodiment of an intervertebralfusion prosthesis 610 is illustrated. The prosthesis 610 comprises aspacer 612, a jacket 614, and four anchors 616.

Referring to FIG. 20B-20C, the spacer 612 and jacket 614 areillustrated.

Referring to FIG. 20D-20E, the anchor 616 is illustrated. The anchor 616is distinguished from the previously disclosed anchor 116 in theconfiguration of the stop feature and locking feature. The anchor 616also comprises a channel 673 and a hook 675 not previously disclosed foranchor 116.

The anchor 616 is generally elongate with a leading end 668 and atrailing end 670 opposite the leading end 668. The stop featurecomprises a flange 674 integral to a dovetail beam 672 at the trailingend 670, similar to the description of anchor 116. The flange 674 isnotched by a channel 673 extending along the dovetail beam 672. Theflange 674 is also enlarged into a hook 675 disposed opposite thechannel 673 on the dovetail beam 672 and opening toward the leading end668. The locking feature comprises a flexible tab 678 integrated on thedovetail beam 672 proximate the trailing end 670 and disposed on thesame side of the dovetail beam as the channel 673. This embodimentprovides the same stop and lock functions described previously for theanchor 116, and provides for unlocking and removing the anchor 616 byinserting an object into the channel 673 to depress the tab 678 againstthe dovetail beam 672 and grasping the hook 675 to remove the anchor616.

Referring to FIG. 21, an alternate embodiment of an anchor 716 is shown.Anchor 716 comprises a flange 774 similar to flange 174 of anchor 116, atab 778 similar to tab 678 of anchor 616, and a channel 773 similar tochannel 673 of anchor 616.

Referring to FIG. 22A-22M, various alternative embodiments are shown ofan intervertebral fusion prosthesis with four anchors.

Referring to FIG. 22A, an alternative embodiment of an intervertebralfusion prosthesis 810 is illustrated. Prosthesis 810 comprises a spacer812 and four anchors 816. Prosthesis 810 comprises a T-shapedinterconnection between spacer 812 and anchor 816. The anchors 816 areat an acute relative angle in only one plane.

Referring to FIG. 22B, another alternative embodiment of anintervertebral fusion prosthesis 910 is illustrated. Prosthesis 910comprises spacer 912 and four anchors 916. Prosthesis 910 comprises adovetail interconnection between spacer 912 and anchor 916. The anchors916 are at an acute relative angle in only one plane.

Referring to FIG. 22C, yet another alternative embodiment of anintervertebral fusion prosthesis 1010 is illustrated.

Referring to FIG. 22D, yet another alternative embodiment of anintervertebral fusion prosthesis 1110 is illustrated.

Referring to FIG. 22E, yet another alternative embodiment of anintervertebral fusion prosthesis 1210 is illustrated.

Referring to FIG. 22F, yet another alternative embodiment of anintervertebral fusion prosthesis 1310 is illustrated.

Referring to FIG. 22G, yet another alternative embodiment of anintervertebral fusion prosthesis 1410 is illustrated.

Referring to FIG. 22H, yet another alternative embodiment of anintervertebral fusion prosthesis 1510 is illustrated.

Referring to FIG. 22I, yet another alternative embodiment of anintervertebral fusion prosthesis 1610 is illustrated.

Referring to FIG. 22J, yet another alternative embodiment of anintervertebral fusion prosthesis 1710 is illustrated.

Referring to FIG. 22K, yet another alternative embodiment of anintervertebral fusion prosthesis 1810 is illustrated.

Referring to FIG. 22L, yet another alternative embodiment of anintervertebral fusion prosthesis 1910 is illustrated.

Referring to FIG. 22M, yet another alternative embodiment of anintervertebral fusion prosthesis 2010 is illustrated.

Referring to FIG. 23A, an alternate embodiment of an intervertebralfusion prosthesis 2110 is illustrated. Prosthesis 2110 resembles anelongated version of prosthesis 110. Prosthesis 2110 may be configuredto fit in one of a right or left lateral side of an intervertebral discspace. Alternatively, prosthesis 2110 may be configured to extendlaterally across an intervertebral disc space.

Referring to FIG. 23B, an alternate embodiment of an intervertebralfusion prosthesis 2210 is shown. Prosthesis 2210 comprises a spacer 2212and two anchors 2216. Prosthesis 2210 comprises a keyhole-shapedinterconnection between spacer 912 and anchor 916. The anchors 2216slidingly engage the spacer 2212 and thread into adjacent bone.

One way to view the teachings set forth above is to characterize certainstructures as an intervertebral spacer means for at least partiallyfilling an intervertebral disc space between adjacent vertebrae afterremoval of at least a portion of an intervertebral disc. In the variousembodiments set forth above, the spacers 112, 212, 512, 612, 812, 912,and 2212 as shown in FIGS. 1-3, 5, 7-8, 11-15, 18-20, and 22-23 can becharacterized as intervertebral spacer means.

Certain aspects of the teachings set forth above can be characterized asjacket means for sustaining spinal loads across opposite sides of thespacer means. In the various embodiments set forth above, the jackets114, 214, 514, and 614, as shown in FIGS. 1-2, 4-5, 7-8, 11-13, and16-20 can be characterized as jacket means.

Certain aspects of the teachings set forth above can be characterized asanchor means for securing the spacer means to adjacent vertebrae so thatthe vertebrae are substantially relatively immobilized against oppositespinal motions. In the various embodiments set forth above, the anchors116, 216, 316, 416, 516, 616, 716, 816, 916, and 2216, as shown in FIGS.1-2, 6-13, and 18-23 can be characterized as anchor means.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the above-described examples can bemixed and matched to form a variety of other alternatives. As such, thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

The invention claimed is:
 1. A bone anchor, comprising: aninterconnection portion to slidingly engage a prosthesis; a fixationportion to fix the anchor to a bone having an expandable leading end andbeing spaced apart from the interconnection portion; and a legconnecting the fixation portion to the interconnection portion, the legincluding a cutting edge capable of cutting through bone.
 2. The anchorof claim 1, wherein the interconnection portion comprises a dovetailbeam.
 3. The anchor of claim 1, wherein the fixation portion comprises aplate oriented substantially perpendicular to the leg.
 4. The anchor ofclaim 1, comprising: a prosthesis lock portion to resist disengagementof the anchor from the prosthesis.
 5. The anchor of claim 4, wherein theprosthesis lock portion comprises a resilient tab integral with theinterconnection portion.
 6. The anchor of claim 4, wherein theprosthesis lock portion is biased to resist disengagement of the anchorfrom the prosthesis.
 7. The anchor of claim 6, wherein the prosthesislock portion is selectively releasable to permit disengagement of theanchor from the prosthesis.
 8. The anchor of claim 1, comprising: a stopportion to limit engagement of the anchor to the prosthesis to apredetermined maximum engagement.
 9. The anchor of claim 8, wherein thestop portion comprises a flange integral with an end of theinterconnection portion.
 10. The anchor of claim 1, wherein the fixationportion comprises a sharpened cutting edge that penetrates the bone whenthe anchor is urged against the bone.
 11. The anchor of claim 10,wherein the cutting edge biases the fixation portion to diverge from theinterconnection portion as the anchor is urged against the bone.
 12. Theanchor of claim 10, wherein the fixation portion resists penetrating thebone when the anchor is urged out of the bone.
 13. The anchor of claim1, wherein the leg comprises an aperture bounded by the interconnectionportion and the fixation portion.
 14. The anchor of claim 1, wherein thefixation portion comprises an aperture.
 15. The anchor of claim 1,wherein the leg is a first leg coupled with the interconnection portionadjacent the leading end thereof, and further comprising a second legconnecting the fixation portion to the interconnection portion andcoupled with the interconnection portion adjacent the trailing endthereof.
 16. A bone anchor, comprising: an interconnection portion toslidingly engage a prosthesis, the interconnection portion including aleading end, a trailing end, and a stop portion adjacent the trailingend to limit engagement of the anchor to the prosthesis to apredetermined maximum engagement in a direction extending between theleading and trailing ends; a fixation portion to fix the anchor to abone having an expandable leading end and being spaced apart from theinterconnection portion; and a leg connecting the fixation portion tothe interconnection portion.
 17. The anchor of claim 16, wherein thestop portion comprises a flange integral with the trailing end of theinterconnection portion.
 18. A bone anchor, comprising: aninterconnection portion to slidingly engage a prosthesis; a fixationportion to fix the anchor to a bone having an expandable leading end andbeing spaced apart from the interconnection portion to fix the anchor toa bone; and a leg connecting the fixation portion to the interconnectionportion, wherein the fixation portion is biased to diverge from theinterconnection portion as the anchor is urged against the bone.
 19. Asystem for spinal fusion, comprising: a porous intervertebral spacersized and shaped to at least partially fill an intervertebral disc spacebetween first and second adjacent vertebrae; and a bone anchorincluding: an interconnection portion to slidingly engage a prosthesis;a fixation portion to fix the anchor to a bone having an expandableleading end and being spaced apart from the interconnection portion; anda leg connecting the fixation portion to the interconnection portion,the leg including a cutting edge capable of cutting through bone,wherein the anchor is sized and shaped to secure the spacer to the firstvertebra so that the spacer and the first vertebra are substantiallyrelatively immobilized against antagonistic spinal motions.
 20. A boneanchor, comprising: an interconnection portion to slidingly engage aprosthesis; a fixation portion having a tapered, expandable leading endand being spaced apart from the interconnection portion to fix theanchor to a bone, wherein a cross-section of at least a portion of thefixation portion has a substantially circular perimeter in a view from atrailing end of the anchor; and a leg connecting the fixation portion tothe interconnection portion, the leg including a cutting edge capable ofcutting through bone.